Huntington's Disease (HD) is a progressive neuropsychiatric disorder produced by premature cell death in the basal ganglia, globus pallidus and to a lesser extent the cerebral cortex. The symptoms of the disease, characterized by progressive involuntary movements and dementia, do not generally appear until the third or fourth decade of life which is usually after child-bearing years. This proposal describes a set of techniques that can be used to clone the HD gene. This effort will involve two phases. The first phase is to narrowly define the genomic position of the disease gene. The second phase is to analyze that region for all possible candidate genes and establish which gene is the HD gene. The current application describes the first phase of this effort. A somatic cell hybrid containing only the short arm of human chromosome 4 in a rodent background will be used to provide chromosome specific DNA. New cosmid cloning vectors, containing unique restriction sites for enzymes that cut human DNA very infrequently, will be used to clone the ends of large DNA fragments. These widely-spaced restriction sites will be sequentially ordered to create a physical linkage map for the short arm region. This physical linkage map will be used to assign the genetic marker G8 (closely linked to HD) to a single restriction fragment. This localizes the HD gene to two regions that flank that site. Genetic markers derived from the DNA cloned at each restriction site junction will be used to test families with defined recombination events between G8 and HD. To ease the analysis of these recombination events and obtain more information, a new type of somatic cell hybrid will be isolated. These hybrids made from the affected mother and recombinant child can be used to establish phase for any maternally heterozygous genetic marker. Since the recombination events between HD and G8 disrupt the linear order of the maternal chromosome, analyzing the order of the maternal and recombinant chromosome with the genetic markers derived from the physical map (which have their linear order defined by that map) will identify genetic and physical sites that are closely linked to HD. Pedigree analysis of any genetic markers closely linked to HD will localize the disease gene to a small genomic area which is the first step to cloning any undefined genetic disorder.